Measuring apparatus



Aug. 9, 1.949. Y v F R, BQOSEY 294753,35?,

MEASURING APPARATUS v FilecLApril 1o, 1947 2 sheets-sheet 1 I. *INVEN-ro- All@ 9, 1949. F. R. BoosEY 2,478,363

MEASURING APPARATUS Filed April 10, 1947 2 Sheets-Sheet 2 Patented ug. Y9, 1,949

MEASURING APPARATUS Frederick Robert Boosey, Letchworth, England, ssignor to The Sigma Instrument Company Limited, Letchworth, England, a British com- Dany Application April 10, 1947, Serial No. 740,637 In Great Britain January 10, 1946 1 Claim. 1

This invention relates to measuring apparatus and is applicable in many fields Where a gauging movement can be employed to produce corresponding variations in the electrical characteristics of circuit elements included in an indicating electric circuit.

The invention is concerned particularly with measuring apparatus of the kind comprising a rst variable impedance and a Second variable impedance, such impedances being relatively differentially variable according to the value that it is desired to measure and each such impedance being separately connected in an A. C. circuit including a rectifier bridge, there being, one bridge in respect of each such circuit so that upon the two bridges D. C. potentialsI develop that vary according to the dilerential variations of thesaid impedances, said rectier bridges being nterconnected to allow a D. C. circulating current to ilow. A galvanometer, connected between the two conductors which inter-connect the two-rectiers, detects the difference between the two output. potentials, the magnitude of the deection being dependent on the magnitude of the difference (zero deiiection signifying equality) and. the direction of the deflection. depending on which is the greater potential, so that such galvanometer may therefore record the direction. and extent of differential variation in said impedances.

For a better understanding of the nature of the invention and to show how the same may be carried into effect reference will now bev made to the accompanying drawings, in.k which,

Figure 1 is an electrical circuit. diagram serving also to illustrate diagrammatically certain apparatus, and

Figure 2 is a diagrammatic representation or certain modified apparatus.

Referring rst to Figure 1, there is.l a referencev anvil I and a gauging anvil 2. The anvil 2 is carried upon a supporting bar 3- which is in turn carried by lath springs. 4 and 5. The latter are secured ina bed plate member 6, the. elements, 3, 4, 5 and 6 constituting effectively the links of. a so-called f our bar chain. Two 4Ll-shaped cores) I and 8 are disposed to co-operate with a further similar pair 9, and I0.. The cores 'I and 8 are secured to the bed, plate 6 whereas the cores 9, and In are mounted` upon a carrier element I I. lA Stationary block I2 is effectively securedl to the bed plate 6, and lies opposite a block I3 that is secured to the carrier element lI. Lath springs I4 arranged in cruciform fashionl are anchored' attheir ends respectively tothe blocks I2 and I3, so as to afford a pivotal support. tor' the block. r3',

- creases;

the axis of the pivot coinciding with the axis of intersection of the cruciform lath springs I4. The cores I and 9 together afford an approximately rectangular magetic circuit having two air-gaps. The cores 8 and Ill afford a similar magnetic -circuit similarly possessing two air-gaps. There are windings I5, I6, I'I and I8 which embrace the arms of the cores I, 8, 9 andlil. The windings I5 and I6 are connected in series, and in a like manner the windings Il and I8 are connected in series.

r1`he carrier element II has an arm I9 which projects through a suitable cut-out in the bar 3. A corresponding arm 20 provided on the bar 3, is constrained to follow the movements of the arm I9 (and vice Versa) by a tension spring 2I, the arm 2lil having a contact piece 22 for engagement with a suitable portion of, or on, the arm I8.

It will now be realised from the description so far Vgiven that when the anvil 2 is moved say upwardly in the performance of a gauging movement, then the :bar 3 is moved upwardly by flexing of the lath springs 4 and 5. Simultaneously an upward displacement of the arm 2e causes the Y arm I9 to be upwardly displaced, whereby the carrier element Il is rocked about the pivotal axis afforded by the cruciform lath springs I4. As a result, the cores 'I' and 9v are relatively approached to one another to reduce the air-gaps between them. The air-gaps 4between the cores 8 and IIJ are at the same time increased. The total: inductance of the series windings i5 and I5 therefore increases whilst the inductance of the series windings I'I and I8 correspondingly de- Hence a diierential change in the inductance as between the two sets of series windings will occur,V the extent of such difierential variation depending upon the extent of linear gauging movement of the anvil. 2.

m The electrical circuit that permits observation of the diilerentialv inductance change will now be described. Essentially the circuit comprises two rectifier bridges. The one bridge has rectiers 30, 3|, 32 and 33 whilst the other bridge has rectiers 34, 35, 36 and 31. It will be observed that the rectiers 3U and 3I both permit passage of current in a direction towards the junction 38 whilst the rectiers 32 and 33 both permit current to pass in a direction away from the opposite junction 39. The arrangement of the rectifiers 34. to 3l of the other bridge is such that the junction 40 is of the same character as regards direction of current flow as the junctiony 39, whereas the opposite junction 4I has the same character as the junction.` 38 relation tov di- 3 rction of current flow. Thus the two rectifier bridges are similarly disposed but are inverted as compared with one another.' The junctions 38 and 49 are connected by a line 42 in which there is a resistance 43. The junctions 39 and 4| are joined by a line 44.

The series connected windings I and I6are on one side joined to one end of the secondary winding 45 of a transformer. secondary winding 45 is joined by a connection 46 to the bridge junction 41. the series connected windings I5 Vand I5 is joined by the connection 48 to the opposite bridge junc- The other end of the A' The otherV side of 4 potential is applied at the bridge junction 41 and 49. It will be clear from the described and illustrated circuit arrangement that the one junction 38 will develop one polarity whilst the other junction 39 will develop an opposite polarity. Let it be supposed that the junction 38 becomes positive, then the 'junction 39 will become negative. The winding 59 will be similarly energised and in a like manner will produce an alternating vpotential across the bridge junctions 52 and 54 lvia the windings I1 and I8. The rectifier bridge is in this case inversely arranged and as a result f negative potential will develop at the junction 49 tion 49. In like manner, the series connected l.

windings I 1, I8 are at one side joined to one end of the secondary winding 59, the other: end of such secondary winding being joined by the connection 5| to the bridge junction 52. The 'other side of the series connected windings I1 and I8 is joined;

by a connection 53 tothe bridge junction 54. There is a source of alternating current supply indicated at 55, such source being connected tol the primary winding 56 of the transformer having the secondary windings 45 and 59.

' An indicating galvanometer G is provided, this galvanometer preferably being of the kind which forms the subject of'rny copending United States patent application Serial No. 740,636, led April 10, 1947. The circuit could of course be ar' ranged to operate in conjunction with other kinds of galvanometer, but the use of the galvanorneter forming the subject of my co-pending patent application is preferred. In the diagrammatic iln lustration of the galvanometer G, it is assumed that the galvanometer is seen in plan. Essentially the galvanometer includes a, deflection coil 51 arranged to move in a field due to concave pole pieces 58. There is a pointerv59 whichcooperates with a suitable scale 6G, and it will be recognised that the galvanometer so far described low the deflection coil however, there is a .control coil 6I which provides the restoring torque for the deilection coil 51. The control coil 6I moves in a eld due to a separate pair of pole pieces62, which produce a iiux distribution that is chosen according to the type of scale 69 that is desired. The control coil 6I is connected for constant excitation from the source 55, in such manner that external variations in the character of the current supplied at the source 55 will be auto-- matically compensated, as will be more fully indicated hereafter. The control coil 6| is joined by connections 63 and 64 with opposite junctions 65 and 66 of a rectier bridge having rectifiers 61, 68, 69 and 10. It will be observed that the rectiers 61 and 68 both permit passage oicurrent to the junction 65 whilstthe rectifiers 99 and 10 both allow current to flow from the junction` 66. The other bridge junctions 1| and 12 are connected across the supply source 55 through a resistance 13 and a condenser-'14.V

The connections just described, servefor the energisation of the control coil 6I, and it remains to indicate that the deflection coil 51 isY joined by connections 15 and 16, the connection 15 be. ing carried to the line 44 whilstthe `connection 16 joins an arm 11 that displaceably contacts and positive potential at the junction 4I. Thus the lines 42 and 44 vwill carry a D. C. circulating current. By adjustment of the arm 11 in relation tothe resistance 43, it will therefore be reference to the connections 15 yand 19.

el Li possible tond a zero potential position with With the arm 11 adjusted in this way no current will flowY in the dellection coil 51. -1

. The supply source 55 provides also an alternating potential across the bridge junctions 1| and 12, via the impedance of the condenser 14 and the resistance 13. Polarity therefore develops at the bridge junctions 65 and 66 so that a direct current is supplied via the connections 63 and 94 to the control coil 5|.

u The descriptionV of the operation of the electric circuit so far given deals with the case where the circuit is energised but gauging is not taking place. It will now be supposed that a work-piece is, inserted between the anvils I and 2 whereby the vanvil 2 makes a gauging movement. Such l. gauging movement produces a correspondingV angular 'movement of the carrier element II, carrying the cores 9 and I9, in the manner previously described. Let it be supposed that as a result of this angular displacementV the air-gapsV between the vcores 1 and 9 are reduced, whilst thoseV between the cores 8 and 'I9 are correspondingly increased. The corresponding differential alteration in the inductances due to the coil pairs I5, I6 and I1, I8 will cause the D. C. potential across thebridge junctions 49 and 4| to increase accordingly whilst that across the junctions 38 and 39 correspondingly decreases. Thus a potential difference as between the lines 15 and 16 now exists depending in magnitude upon the eX- tent of angular vdisplacement of the cores 9 and I9, and depending'in direction upon the direction of angular displacement of the said cores. The deflection coil 51 of the galvanometer G thus produces a movement of the pointer 59 with referencefto the scale 69, and thereby gives the de-` sired indication of the gauging movement.

In the above description reference has been made to the connection of the bridge junctions 1| and 1'2 across the source 55 (via the resistance 13 and capacitance 14). Alternatively the transformerA 56 could'have an additional secondary winding for supply of the junctions 1| and 12.

In Figure 2 a more compact form of the differentially variable impedances, is shown. Essentially there is a'lower plate |99 associated with'a plate |9| whichvmay rock relatively thereto. Rocking is permitted by the pivot pillars |92 and |93 which are held together by tension springs |94 and |95. Pole-pieces |96, |01 and |98 on one plate co-operate with pole-pieces I 99. III) and III on the other plate. VThe poles |01 andv |I9 arecommon to both magnetic circuits and there are-coils ||2 and |I3 which permit the differential impedance variation in a manner thatWll be clear from the description herein# before. It will be noted that in this construction' two instead of four coils are employed, but the sensitivity is thereby reduced.

The restoring torque exerted by the control coil BI will of course depend for its constancy,7 upon unchanging voltage and frequency values in the supply at the source 55. If the voltage of the source 55 should change then there would clearly be an alteration in such restoring torque. For an increase in voltage the tendency will be for the restoring torque to increase but on the other hand an increase in voltage would result in an increased D. C. potential at the bridge junctions 38, 38 and 40, 4| with corresponding increase in the potential as between the lines 1'5 and '16. Hence there will be compensation for a voltage increase of the source 55. There will similarly be compensation for a voltage decrease of the source. As regards frequency changes of the source, an increase in frequency will produce greater sensitivity in the differentially variable inductances for the reason that inductive reactance is a function of frequency (with, of course, all other factors maintained constant). It will be appreciated that capacitative reactance is, however, an inverse function of frequency, and hence the impedance provided by the condenser 14 will tend to fall with increase in frequency. Thus the current in the control coil will increase so as to off-set the increased sensitivity of the differentially variable inductances. In this manner frequency compen sation is obtainable depending upon correct choice of the value of the condenser 14.

I claim:

Measuring apparatus comprising a first variable inductance choke possessing a choke winding and a variable air-gap core, a second similar variable choke, a mechanical connecting inember between the cores of said first and second variable chokes, measuring means associated with said mechanical connecting member to displace the same according to linear dimensions that are gauged and thereby differentially alter the air-gap setting as between said first vari able choke and the second variable choke, a first four-armed rectifier bridge network having a first and second pair of oppositely situated bridge junctions, a series connection from the choke winding of said first variable choke to one of the junctions of said first pair, a source of alternating current supply connected to supply alternating current to the winding of said first variable choke and to the other junction of said first pair of bridge junctions, said first rectifier bridge network having the rectifiers thereof disposed to cause persisting polarity to develop at said second pair of junctions thereof, a second rectifier bridge network similar to the first and possessing also a first and a second pair of opposite bridge junctions, a connection from one of said first pair of bridge junctions of the second rectifier network to the choke winding of said second variable choke, connections from this latter choke winding and the second junction of said first pair of said second rectifier network to said source of alternating current thereby to cause the second pair of junctions of said second rectifier network to develop a persisting polarity, two connecting lines between said second pairs of bridge junctions of both rectifier networks each connecting line extending between junctions of opposite polarity, a potential divider included in one of said connecting lines such potential divider possessing a dividing arm, a galvanometer having a defiection coil connected with the dividing arm of the potential divider and with the other connecting line which does not contain said potential divider, a restoring coil connected for exerting restoring torque upon said deflecting coil of said galvanometer, means for producing a magnetic field for said deflection coil, means for producing magnetic field for said restoring coil, a third rectifier bridge network similar to the other two and possessing two pair of oppositely disposed bridge junctions, connections from said source of alternating current to supply current across one pair of said junctions of the third bridge rectifier network, a capacitive impedance included in the connections between said alternating current source and the pair of the bridge junctions of said third bridge rectifier network, and connections between the other pair of junctions of said third rectifier bridge network to said restoring coil.

FREDERICK ROBERT BGOSEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,240,184 Hathaway Apr. 29, 1941 2,394,079 Langer Feb. 5, 1946 2,421,420 Hathaway June 3, 1947 2,434,547 Browne Jan. 13, 1948 FOREIGN PATENTS Number Country Date 405,043 Great Britain Feb. 1, 1934 548,105 Great Britain Sept. 24, 1942 556,607 Great Britain Oct. 13, 1943 

